Rett Syndrome (RS) affects girls in many ethnic groups with a consistent clinical pattern most evident during ages 1-4 with subsequent stabilization. Pathogenesis of RS is unknown, but results from our previous grant period provided the overall hypothesis that a genetic defect disrupts subsets of neurons and their interconnections during rapid brain growth when synapses are formed and pruned. Three interactive projects will test this hypothesis with the ultimate goal of providing treatment. Project 1 is designed to determine the natural history of this disease by clinical and volumetric MRI analysis (Project 3). Novel strategies (2D gel electrophoresis, high density cDNA arrays, and RDA) will attempt to detect a marker. Olfactory receptor neurons from nasal biopsies will permit study of deficits in neurogenesis, and maintenance in culture. Together with information from Project 2, new therapeutic approaches will be tested in controlled clinical trials, and supported by Neuroimaging studies in Project 3. Projects 2a and b will focus on alterations in neurotransmitter receptors and dendritic proteins by autoradiography and quantitative methods in postmortem brain tissue, and a mouse lesioned to induce cholinergic deficits with alterations in cortical morphology that resemble those in RS. The hypothesis that elevated glutamate levels are related to abnormalities in glutamate reuptake will be tested. Restoration of cortical deficits in the mouse model will be studied by treatment with anticholinesterase inhibitors, and delivery of growth factors through genetically engineered endothelial cells, which as implications for future application in patients. Project 3 will establish the status of the cholinergic system in vivo by SPECT measurement of vesamicol binding as a function of age, and determine effective dose of anticholinesterase inhibitors by PET and clinical correlation. MRS will determined changes in glutamate with age, and efficacy of therapy with glutamate antagonists. Volumetric MRI studies will be assessed longitudinally for age related and regional changes. The complementary interdependent programs should help to delineate the pathogenesis, detect a diagnostic marker, and provide rational therapies in RS.